The present invention relates to a method of false twist texturing a synthetic yarn to a crimped yarn, as well as the resulting crimped yarn.
To assimilate the characteristics of synthetic textile yarns to those of yarns from natural fibers, such as wool or cotton, it is known to improve the spun synthetic yarns in a texturing process. In this process, the synthetic filament strands, which form the yarn, are crimped, so that the yarn obtains a more textilelike appearance and the therewith connected characteristics. Such a process is known, for example, from JP 05311527 A, wherein the multifilament yarn is drawn in a draw zone with the aid of a heated draw pin, and subsequently, textured in a false twist zone. For producing the crimp, a false twist is produced in the yarn, which is set in the false twist zone by means of a heating device. Subsequently, the crimped yarn is wound to a package.
In the known method, a crimped yarn is produced, which has a very uniform structure with little bulk. As a result of hot drawing the filaments on the draw pin, a relatively closed combination of filaments is created, which results in little bulk and, thus, a low bulkiness of the crimped yarn. This imparts to thus-produced crimped yarns a more artificial appearance.
It is therefore an object of the invention to further develop the initially described method such that a crimped yarn is produced, which comes as close as possible to the character of natural fibers, as regards bulkiness, hand, and appearance.
The above and other objects and advantages of the present invention are achieved by the provision of a false twist texturing member wherein the synthetic yarn advances at a delivery speed w1.1 and under a low absolute yarn tension F1 of maximally 5 cN to a heated draw pin in a draw zone. In the draw zone, the yarn undergoes drawing by looping about the draw pin at a looping angle xcex1 less than 270xc2x0, and it is withdrawn by a downstream feed system. In this process, the yarn tension F2 in the yarn path downstream of the draw pin, is substantially greater than the yarn tension F1 upstream of the draw pin. The feed system advances the yarn at a speed w1 into the false twist zone. For purposes of drawing the yarn in the draw zone, this advancing speed w1 is greater than the delivery speed w1.1. In the false twist zone, the false twist is set at a temperature of more than 180xc2x0 C. In this process, the yarn undergoes in the false twist zone a slight subsequent drawing. However, the withdrawal speed w2 is not greater than 1.1 times the advancing speed w1. Subsequently, the crimped yarn is wound to a package.
The method of the present invention is based on the recognition that the adjustment of the yarn tension in the draw zone upstream of the draw pin has a direct influence on the evenness of the drawing. Thus, it has been found that in particular in the case of low yarn tensions, the yarn is caused to flutter as it comes into contact with the draw pin. These flutters lead to an irregular thermal stress of the yarn on the draw pin and, thus, to an irregular drawing of the yarn. In this connection, use is made of the effects, in that as the yarn contacts the hot draw pin, the evaporating volatile components of the yarn exert forces on the draw pin. In relation to the low yarn tension, these forces are effective crosswise to the direction of the advancing yarn, and generate a fluttering motion of the yarn on the draw pin. After false twist texturing in the false twist zone, the uneven drawing and the irregular thermal stress of the yarn become effective in such a manner that the synthetic filaments intertwine irregularly, so that yarn lengths of a loose combination of filaments alternate with yarn lengths of a closed combination of filaments. In this connection, the loose combination of filaments forms a larger yarn cross section than the tight combination of filaments, so that a crimped yarn develops with a thick-thin effect.
To make the change of the filament combination in the crimped yarn reproducible, the yarn tension F2 upstream of the feed system may be adjusted to a range from 0.5 cN/dtex to 1.2 cN/dtex for purposes of withdrawing the yarn from the draw zone.
During the drawing of the yarn, the draw pin is heated to a temperature ranging from about 80xc2x0 C. to 160xc2x0 C., preferably above 100xc2x0 C. In this process, the yarn partially loops about the draw pin at an angle in the area of at least 90xc2x0. This makes it possible to influence the crystallinity of the filament strands, so that the differences in the filament combinations exhibit a high stability.
To make drawing uniform, the yarn undergoes a subsequent drawing in the false twist zone. In this connection, it is especially advantageous to adjust the subsequent drawing so that ratio w2/w1 is between about 1.03 to 1.06.
To ensure that the filament strands receive an adequate crimp even in the yarn lengths with a closed combination of filaments, a friction false twist unit with a plurality of friction disk has shown to be especially useful for producing the false twist on the yarn.
To produce less highly elastic crimped yarns, the yarn may undergo an aftertreatment by heating, after receiving the false twist and before being wound to the package, so as to enable a shrinkage of the yarn.
The method of the present invention makes it possible to produce a crimped yarn, which has characteristics that are otherwise known only from novelty yarns. The natural character of the yarn crimped according to the invention is especially enhanced by the changes in the filament combinations, which occur irregularly in sequence and size. The irregular yarn cross section of the crimped yarn according to the invention becomes even substantially more prominent in the dyeing of the filament yarn or in fabrics made therefrom. Not only do the yarn lengths with the open combination of filaments exhibit a color reproduction that is quite different from the yarn lengths with the closed combination of filaments, but the yarn lengths with a closed filament combination also exhibit a higher crystallinity than the yarn lengths with the open filament combination. With that, a structured dyeability is realized, which leads in a fabric to a uniform color structure. The different yarn segments may have a length from few millimeters to several centimeters.
Because of the yarn lengths with the open combination of filaments, such crimped yarns can be used for producing in an advantageous manner a composite yarn consisting of a plurality of individual yarns, for example, from different polymers. In this method, at least one of the yarns is textured in accordance with the invention, before being combined to the composite yarn. The thus-produced composite yarns distinguish themselves likewise by their natural character. It is preferred to combine the yarns by an air entanglement by means of an entanglement nozzle. In this process, an air jet is directed substantially crosswise to the yarn bundle, so that the filaments of the yarns intertwine.
To produce a crimped yarn of the present invention, an apparatus has proved to be especially useful which comprises a delivery system, a draw pin, a first feed system, a heating device, a cooling device, a false twist unit, a second feed system, and a take-up device. A yarn guide is arranged in the yarn path downstream of the draw pin, which is made adjustable for setting a predetermined looping angle of the yarn about the draw pin. With that, it is possible to adjust on the draw pin the characteristic, irregular draw ratio within a wide range by changing the looping of the yarn.
Preferably, the yarn guide is adjusted on an arcuate guideway, which is designed and constructed at a substantially constant distance from the circumference of the draw pin. With that, the yarn tensions adjusted in the draw zone remain substantially unchanged, even when the looping angle is changed.